In a number of applications, light-weight, high-strength structural members are required, for example in motor vehicles and aircraft as well as in various devices such as home appliances and the like. A number of composite materials have been proposed in the past as structural members, such as exotic light-weight alloys. In most applications, however, mass reduction must be balanced against the cost of the product to the consumer. Thus, there is a need for providing strength without significantly increasing materials and labor costs. Moreover, reinforcement techniques are needed which can be adapted to existing geometries of structural parts, obviating any requirement for fundamental design changes.
As examples of reinforcement techniques, the present inventor has disclosed a number of metal/plastic composite structures for use in reinforcing motor vehicles components. In U.S. Pat. No. 4,901,500, entitled "Light-weight Composite Beam," a reinforcing beam for a vehicle door is disclosed which comprises an open channel-shaped metal member having a longitudinal cavity which is filled with a thermoset or thermoplastic resin-based material. In U.S. Pat. No. 4,908,930, entitled, "Method of Making a Torsion Bar," a hollow torsion bar reinforced by a mixture of resin with filler is described. The tube is cut to length and charged with a resin-based material.
In U.S. Pat. No. 4,751,249, entitled, "Reinforcement Insert for a Structural Member with Method of Making and Using the Same," a precast reinforcement insert for structural members is provided which is formed of a plurality of pellets containing a thermoset resin with a blowing agent. The precast member is expanded and cured in place in the structural member. In U.S. Pat. No. 4,978,562, entitled, "Composite Tubular Door Beam Reinforced with a Syntactic Foam Core Localized at the Mid Span of the Tube," a composite door beam is described which has a resin based core that occupies not more than one-third of the bore of a metal tube.
In U.S. Pat. No. 5,575,526, entitled "Composite Laminate Beam for Automotive Body Construction," a hollow laminate beam characterized by high stiffness-to-mass ratio and having an outer portion which is separated from an inner tube by a thin layer of structural foam is described. In U.S. Pat. No. 5,755,486, a W-shaped carrier insert reinforcement which carries a foam body is described for use in reinforcing a hollow beam.
In U.S. patent application Ser. No. 08/644,389, filed May 10, 1996, entitled "INTERNAL REINFORCEMENT FOR HOLLOW STRUCTURAL ELEMENTS," now abandoned, the present inventor discloses an I-beam reinforcement member which includes an external foam layer. The I-beam, as in the case of most of the foregoing reinforcements, involves a preformed structural insert which is then inserted into a hollow structural member.
It is also known to increase strength of a laminate structure by bonding together flat metal plates using an intervening layer of resin. For example, it is known to form a metal laminate sheet for use as a floor panel member which comprises a pair of flat metal sheets having an intervening layer of asphalt or elastic polymer.
Although filling the entirety of a section with plastic foam does significantly increase section stiffness (at least when high-density foams are utilized), this technique also may significantly increase mass and thus part weight, which, as stated, is an undesirable feature in most applications. In addition, filling a section entirely with foam may be prohibitively expensive and creates a large heat sink. And, although increasing the metal gauge of a section or adding localized metal reinforcements will increase stiffness, as the metal thickness increases, it is more difficult to form the part due to limitations of metal forming machines.
Accordingly, it would be desirable to provide a low-cost technique for reinforcing a channel-shaped structural member without proportionately increasing the mass. It would also be desirable to provide a method of reinforcing an existing channel-shaped member which does not require any fundamental design changes to the member. The present invention provides channel-shaped members which have increased strength with moderate increases in mass and without the use of high volumes of expensive resins. The present invention further provides a method for reinforcing existing structural parts without redesigning the geometry of the part. It has been found that the present invention increases section stiffness and provides vibration dampening in channel-shaped sections in a highly efficient and reproducible manner.